Electrical signal cables that connect electronic devices include one or more signal conductors (e.g., one or more twisted pairs of copper wires, or a copper core). Electromagnetic interference (EMI) can introduce electrical noise into the signal conductors, which can weaken and potentially corrupt the signals being transmitted thereon. Shielded electrical signal cables (“shielded cables”) can be used to reduce the amount of electrical noise that is introduced into the signal conductors and maintain the integrity of the electrical signals that are transmitted between electronic devices.
In a typical shielded cable, the signal conductors are covered with an insulating sheath, followed by a conductive shield and an outer jacket. The conductive shield is often grounded at one or both ends of the shielded cable, and serves to contain EMI emitted by the signal conductors and shield the signal conductors from external electrical events.
Grounding both ends of a shield of a shielded cable can introduce a ground loop between the connected electronic devices. For example, two electronic devices that are connected by a shielded cable may use separate power connections, creating a difference in their respective ground potentials. Consequently, a ground loop can be formed where ground current is introduced into the shield of the shielded cable and flows between the electronic devices to achieve equal potential. Such a ground loop can introduce noise into the signal conductors, as the shield can both emit and receive EMI. In addition, the ground loop can present a shock hazard, as exposed components of the electronic devices that are seemingly at ground potential can become energized. In the context of signal cables used to connect sensitive electronic devices in critical applications, such as electronic devices in mainframe computer systems, the noise introduced into the signal conductors can corrupt the data being transmitted thereon, potentially resulting in errors and system down time. Further, the coupled EMI from the ground loop can prevent concurrent system upgrades and related maintenance activities from being safely performed. Grounding only one end of the shield eliminates the ground current path through the shield, but the shield can still introduce noise into the signal conductors by emitting and receiving EMI, particularly at radio frequencies.